BYR eS tractural and Physiological Botany. 
in the sugar, and is believed to be always present in the air 
in the form of invisible dust. Ifa small quantity of yeast is” 
added toa large quantity of a clear saccharine "fluid, and 
the fluid kept warm, it will gradually become more and more 
turbid, and a scum of yeast will collect, containing a pro- 
digious quantity of Zorula-cells. The ordinary mode of re- 
production is by what is termed budding (Fig. 402, p. 270), 
each cell giving rise to minute buds, which grow rapidly, 
attain the size of the parent-cell, and eventually become 
detached, but not generally until they have themselves de- 
veloped a second generation of buds. They very commonly 
_ adhere together in the form of heaps or strings. A second, 
Dut rarer, mode of multiplication is by exdogenous division, 
the protoplasm of a‘cell dividing into usually four masses, 
each of which surrounds itself by a cell-wall; and the 
daughter-cells are eventually set free by the dissolution of 
the wall of the parent-cell. This is a form of free cell- 
formation (see p. 33). In order to show that the substances 
of which the Zoru/a consists, protein, cellulose, and fat (oil), 
were not present in the nutrient fluid, but have been manu- 
factured by the yeast-fungus out of it, it is best to take a 
nutrient fluid of definite chemical composition, a convenient 
one being that known as ‘ Pasteur’s solution.’! The power 
of constructing protein out of such a substance as ammonium 
tartrate, and the investment of the protoplasm by a con- 
tinuous coat of cellulose, are the chief properties which 
determine the Zorula to be a vegetable. It allies itself to 
Fungi in containing neither starch nor chlorophyll, and hav- 
‘ing consequently no power of decomposing carbon dioxide. 
In the process of fermentation nearly the whole of the sugar 
is converted into an equal weight of alcohol and carbon 
dioxide; but a small quantity of glycerine and succinic acid 
’ Potassium phosphate, 2 parts ; calcium phosphate, 2 parts ; mag- 
nesium sulphate, 2 parts; ammonium tartrate, 100 parts ; cane sugar, 
1,500 parts ; water, 8,394 parts. te 
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